1. Field of the Invention
The present invention relates to a heater incorporated in a laser printer, for example, for thermally fixing toner transferred onto recording paper.
2. Description of the Related Art
Conventionally, liner heaters are used in e.g. laser printers for heating recording paper to thermally fix the transferred toner to the recoding paper. An example of conventional heaters is disclosed in JP-A-2007-121955.
FIGS. 8 and 9 of the accompanying drawings show a heater as a reference example for better understanding of the present invention. Specifically, the illustrated heater X includes a substrate 91 having an upper surface formed with a pair of resistors 92 extending in parallel to each other in Direction x. On the substrate 91, a pair of electrodes 92 are formed near the respective ends of the elongated substrate 92. The electrodes 92 are connected with the resistors 92 by wiring portions 93. The wiring portions 93 have junctions 93a extending in parallel to the Direction y. The resistors 92 and part of the wiring portions 93 are covered by a protective film 95. The protective film 95 can be formed by screen printing to make a film of glass material with a squeegee moved in Direction x, and then sintering the film.
In the above method, however, the squeegee is moved to go over the junction 93a, and at this time the supply of the glass material tends to be insufficient at the shoulder portion of the junction 93a. In this case, a crack 95a as shown in FIG. 9 may often appear in the sintered glass material or the protective film 95. Unfavorably, the crack 95a can lower the withstand voltage of the protective film 95.